US6259180B1 - Motor including embedded permanent magnet rotor and method for making the same - Google Patents

Abstract

An electric motor including a permanent-magnet rotor having embedded magnets held in place by several segments. The embedded magnets are secured by segments including non-circular openings near their centers. Several non-magnetic, non-conductive bars extend through the non-circular openings of the segments to secure the segments in relation to the shaft. The motor is capable of producing high torque while only requiring a minimum amount of space.

Description

This is a divisional of copending application Ser. No. 09/084,562, filed on May 26, 1998, now U.S. Pat. No. 6,005,318 and which is a divisional of prior application Ser. No. 08/675,399 filed Jul. 2, 1996, now U.S. Pat. No. 5,771,563 issued Jun. 30, 1998, which is a division of application 08/191,957 filed Feb. 4, 1994, now U.S. Pat. No. 5,554,900 issued Sep. 10, 1996.

FIELD OF THE INVENTION

This invention relates to an electric motor including a permanent-magnet rotor having embedded magnets held in place by several segments. More specifically, the invention relates to a motor capable of producing high torque while only requiring a minimum amount of space.

BACKGROUND OF THE INVENTION

Synchronous electric motors having permanent-magnet rotors have existed for some time. Many of the rotors that have been used in such electric motors have magnets that are mounted at the periphery of the rotor surface. In these motors, the rotor typically is-made of a magnetically conductive material such as iron or the like. The magnetic flux available to produce force in connection with the magnetic fields in the stator is proportional to the surface area of the magnets on the outer surface of the rotor. In these motors, great care must be taken to mount the magnets in precise relation to the axis of the rotor and so as to maintain a smooth outer surface.

In operation, the flux lines from the magnets in these motors link across an air gap to the stator. The magnets are arranged so that adjoining rows of magnets have opposite magnetic poles facing outward. Thus, around the outside circumference of the rotor, the rows of magnets are arrayed north to south to north, and so on. Typically, the rows are also slightly skewed relative to the stator or the stator is slightly skewed relative to the rotor so as to minimize cogging that occurs as the magnets line up with the respective teeth of the stator. Since total magnetic flux for a magnet is proportional to its surface area, the total available torque for these types of motors is directly linked to the total available surface area of the outside of the rotor. Thus, this rotor arrangement is most useful where either the size of the motor (size of the diameter of the rotor) does not need to be small or the total available torque does not need to be large.

There are some motors where the permanent magnets are not mounted at the outside periphery of the rotor. An example of such a motor is shown in U.S. Pat. No. 4,697,114, issued Sep. 29, 1987, to Amemiya et al. In these motors, the permanent magnets are secured between magnetically conductive wedges which are secured in fixed relation to the shaft of the rotor. The wedges in these motors sometimes consist of sets-of laminated plates held in place by fastening bolts that extend through them parallel to the axis of rotation of the motor and attach to steel end plates which are securely fitted to the shaft. In these motors, the inner surfaces of the wedges and permanent magnets are radially spaced from the shaft the entire length of the magnetized rotor.

In the aforementioned motors the diameter of the rotor must be sufficiently large to accommodate the air gap between the shaft and the magnets and wedges. This presents apparent problems in a lower available torque for a given diameter rotor and a larger overall size. In addition, the manner of mounting and the positioning of the magnets and wedges would appear to adversely affect the response time of the motor to rapid changes in the signal input (stiffness) along with providing relatively high inertia, eddy currents and diminished rotor efficiency.

In control systems, it is often desirable to use small high torque devices to operate various mechanical systems. In the past, where high torque was required but space was limited, system designers often opted to usehydraulic systems because of the lack of electric motors with sufficiently high torque to size ratios. As a result, there has been a need for an-electric motor with high torque that can be used in relatively small spaces.

In applications such as robotics and the like, where response time is critical, there is additional need for electric motors that have high stiffness while not requiring a significant amount of space. In addition, such applications often require that the control system maintain a high energy efficiency.

Accordingly, one object of this invention is to provide a small electric motor including a permanent-magnet rotor having embedded magnets which has high torque to size ratio.

A related object of the invention is to provide an electric motor including a permanent-magnet rotor having embedded magnets which has high stiffness while requiring a minimum amount of space.

Another related object of the invention is to provide an electric motor including a permanent-magnet rotor having embedded magnets which achieves high torque and stiffness while maintaining high efficiency.

Another related object of the invention is to provide an electric motor including a permanent-magnet rotor having embedded magnets which achieves smoothness of operation at low speeds.

SUMMARY OF THE INVENTION

A feature of the invention is an electric motor including a permanent-magnet rotor having embedded magnets secured by segments including non-circular openings near their centers.

Another feature of the invention is an electric motor including several non-magnetic, non-conductive bars which extend through the non-circular openings of the segments to secure the segments in relation to the shaft.

Another feature of the invention is an electric motor where the opening near the center of the segments is generally shaped like an elongated diamond.

Another feature of the invention is an electric motor where the segments are in abutment with the shaft.

Another feature of the invention is an electric motor where the shaft is constructed of non-magnetic material, such as stainless steel.

Another feature of the invention is an electric motor where the securing bars are formed of high tensile strength fiberglass.

Still another feature of this invention is a method for assembling an electric motor including a permanent magnet rotor having embedded magnets.

Another feature of this invention is a method for assembling an electric motor wherein the rotor shaft is force fit into the center of an assembly including the segments, magnets, bars and retainer rings so that rotor acts as a single beam in operation.

Other objects and advantages will become apparent from the following detailed description when taken in conjunction with the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partially in section, of an electric motor including a permanent-magnet rotor having embedded magnets and employing teachings of the present invention.

FIG. 2 is a sectional view of the motor taken alongline2—2 of FIG.1 and enlarged to show greater detail.

FIG. 2A is an enlarged plan view of a lamination used in forming the segments of the rotor of the motor in FIG.1.

FIG. 3 is a plan view of a retainer ring lamination used in the rotor assembly of FIG.1.

FIG. 4 is a partial sectional view of the rotor of FIG. 1 taken alongline4—4 of FIG.2.

FIG. 5 is an enlarged schematic perspective of the rotor showing one axial set of the segments related embedded magnets, and supporting bars.

FIG. 6 is an exploded view of a shaft used in the rotor assembly of FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention will be described in connection with a preferred embodiment, it will be understood that the invention is not limited to that embodiment. On the contrary, the invention covers all alternatives, modifications and equivalents within the spirit and scope of the invention as defined by the appended claims. For example, the preferred embodiment is described in terms of an electric motor; however, the invention herein may take the form of a motor or a generator.

Turning first to FIG. 1, the motor assembly generally indicated as8 includes anelectrical motor10 within anouter housing20 and aterminal box30 which are connected to one another as bymachine screws40. Themotor10 further includes a stator generally indicated at15 and a rotor generally indicated at17. Theterminal box30 includes acover50, secured byscrews60, which has an opening (not shown) through which a power supply (not shown) extends to power themotor10. As shown, wires pass through aligned openings in thehousing20 and the base of theterminal box30. The first set of wires, referred-to hereinafter to asstator lead wires65, connects withstator windings70 within thestator15. As shown, there are a total of sixstator lead wires65 which provide for Y or Δ three-phase operation of themotor10. Although the preferred embodiment provides for three-phase operation, it is noted that other multi-phase or single phase configurations could be implemented.

As shown in FIG. 1, therotor17 includes adrive shaft80 which rotates about a central axis, being rotatably supported by aforward bearing90 and a spacedrear bearing100. Thebearings90 and100 are supported on afront end plate110 and an interior supportingplate120, respectfully. Thefront end plate110 secures and locates the bearing90 by clasping the bearings with aclamping piece130. Theclamp piece130 is secured by means of a set ofscrews135 which are accessible from the front of theplate110.

Front end plate110 attaches to anintermediate casing140 by means ofscrews150 near the outer edges of thefront end plate110 and the front edge of thecasing140. Thehousing140 also is secured to theinterior supporting plate120 by screws which extend through the housing. Of course, in any circumstance where screws are described to secure two component pieces together, any appropriate connecting device may be used such as bolts, rivets, or an integrated assembly weld. Arear end plate160 is secured to theinterior supporting plate120 so as to define an enclosedrear area162 therebetween. Mounted within this rear area and in near proximity toshaft80 is a brushless tachometer andcommutator170 and/or other sensor which produces a signal indicative of the speed of rotation and/or position of theshaft80. As shown in FIG. 1, the brushless tachometer andcommutator170 includessignal wires180 which extends into theterminal box30 and connects with the appropriate circuitry which ultimately powers thestator windings70. The brushless tachometer andcommutator170 is used to monitor position and/or speed of therotor17 and is an integral part to any application where themotor10 is used as a servo. In the preferred embodiment, the brushless tachometer andcommutator170 may be of the kind produced by Servo-Tek Product Companies as TACHSYN® model number T6621) for a six pole motor.

FIG. 2 shows a cross section of therotor17,stator15 andintermediate housing140. Thestator15 includes astator core190 which is comprised of a number of laminations each having substantially the same dimensions. As shown, thestator core190 has thirty-six teeth200 (only one of the teeth shown in FIG. 2 is numbered) which extend inwardly to form a circular cylindrical contour at an inner diameter. Theteeth200 are substantially equidistant from one to the next around the inner circumference and, as such, there are six stator teeth per every 60 degrees with respect to the center axis.

In an exemplary embodiment, the diameter of the inner contour of thestator core190 may be very small. The distance between theteeth200 of thestator core190 along the inner circumference may be correspondingly small. The dimensions of thestator core190 can-be as small as manufacturing procedures permit. Further, in the preferred embodiment, theteeth200 are skewed by one tooth over the length of therotor17. Skewingteeth200 in this way minimizes torque ripple and provides for smooth operation at low speeds and prevents cogging.

In order to facilitate the magnetic circuit with therotor17, each lamination of thestator core190 is made of a material that exhibits high magnetic conductivity and low hysterisis losses, such as magnetic silicon steel. In addition, each lamination is electrically insulated so that eddy currents are limited. In the preferred embodiment, each lamination of thestator core190 is stamped from 2-3% silicon steel and laminated with a non-conductive coating, such as M36 steel with C5 coating sold by Tempel Steel. Although the laminations of the preferred embodiment are produced using a stamping process, it will be recognized that other processes may be used.

To further facilitate the magnetic circuit, the inner ends of theteeth200 of thestator core190 are broadened circumferentially. Theintermediate housing140 is formed separately of a non-magnetic material such as aluminum, stainless steel, etc.; however, magnetic materials may be used. In this manner, the magnetic circuit is structured so as to obtain maximum efficiency. The stator windings70 (not shown in FIG. 2) fill the spaces between theteeth200 of thestator core190, from the outer most radial end to the inner area adjacent the broadened inner end surfaces of theteeth200.

Referring to FIGS. 2,4 and5, the illustratedrotor17 includes the centralaxial drive shaft80 and a plurality ofsegments210 corresponding to a multiple of the number of poles in the motor, e.g., at least sixsegments210 for a six-pole motor. Additional sets of the segments may be added in axial alignment with the first set about the center shaft, depending upon the size of the individual components and the space and power parameters for the motor. Therotor17 includes three axially aligned sets of six segments, with only one segment and related magnets of each set being shown in the schematic illustration of FIG. 5 for clarity. This embodiment optimally produces 13 Nm of torque with therotor17 having an outside diameter of approximately 49.5 mm and three sets of segments as shown in FIGS. 4,5 and6. Theindividual segments210 are supported on securingbars230. Thebars230 extend parallel to the axis of therotor17 throughcentral openings270 in thesegments210 and are supported byretainer rings280 which are affixed to and supported on theshaft80. The retainer rings280 (see FIG. 3) include at least the end retainer rings280 as part of the end assemblies at each end of therotor17, with additional retainer rings282 between each set of thesegments210 when therotor17 includes multiple sets as in the illustrated embodiment.

Themagnets220 are thin flat rectangular magnets each magnetized through its thickness so that its opposite poles are at its opposite major planar faces. Onesuch magnet220 is positioned at each interface betweenadjacent segments210 as best seen in FIG.2 and is held in position by engagement of the respective abuttingsegments210. Each of themagnets220 thus is disposed to extend along and parallel to theshaft80 over the length of therespective segments210 and radially of the shaft, i.e., with its central plane extending parallel to and radially of the axis of theshaft80. Themagnets220 are oriented such that like poles abut each side of eachsegment210 whereby thesegments210 are polarized alternately N-S progressively about the circumference of therotor17. Thus, any single magnetic circuit made by themagnets220 utilizes part of one segment and part of the adjacent segment in connecting with thestator15. Themagnets220 need be of only a minimum thickness to provide the minimum physical strength necessary for reasonable handling and mounting, i.e., to avoid undue fragility of the magnet elements per se. Eachmagnet220 extends from aninner edge221 closely adjacent the surface of theshaft80 to an outer edge which is adjacent the outer edge of thesegments210 and thus the surface of therotor17, being separated therefrom only by narrow retainer protrusions orears260 of thesegments210 which partially overlie the outer edges of themagnets220 for radial retention purposes. The air gap between the opposed retainingears260 should be slightly greater than the air gap between therotor17 and thestator15 to insure directing of the magnetic flux across the air gap to the stator instead of crossing between the rotor segments. In an alternative embodiment, recesses are provided along the sides of thesegments210 which face themagnets220. In this alternative embodiment, shims are inserted into the recesses to position and grip themagnets220.

In the illustrated rotor, thebars230 hold thesegments210 in place with their inner edges firmly seated against the surface of theshaft80. Theshaft80,segments210,bars230 and retainer rings230,232 thus form an integrated structure which provides substantial strength and stiffness even with ashaft80 of relatively small diameter. This, in turn, permits usingradial magnets220 andsegments210 of large radial extent relative to the outside diameter of the rotor, thereby providing greater available flux with good flux control and attendant high power potential with a small rotor in a small motor.

Each of thesegments210 is comprised ofstacked laminations212 having substantially the same configuration and dimensions. As shown in FIG. 2A, eachlamination212 is generally pie-shaped in configuration and includes an inner concavecurved edge240 to conform to the outer circumferential surface of theshaft80 and an outer convexcurved edge250 to conform to the outside circumferential surface selected for therotor17. That is,curved edge240 defines an arc of a radius substantially corresponding to the radius of theshaft80, and thecurved edge250 defines an arc corresponding to the design radius of therotor17.

Eachlamination212 further includes anon-circular opening270 formed near the center of the lamination (as measured radially betweenedges240 and250). Theopening270 is of a generally elongated diamond shape. It is. symmetrical about the center radius of thelamination212 and oriented with its major axis extending radially of the lamination, being of a length and position to substantially bifurcate thelamination212 into symmetrical portions at each side of theopening270. Of course, opening270 could be in the form of other shapes such as a rectangle, triangle or other radially elongated geometrical shape. The inner twoadjacent sides272a,272bof the illustratedopening270 are substantially at 30 degrees relative to each other as are the two outeradjacent sides274a,274b. Where the two inner and outer sides connect, they form an included angle of 120 degrees. As shown, the inner andouter corners276,278 ofopening270 are rounded. In the preferred embodiment, theinner corner276 is of substantially greater radius of curvature than theouter corner278. By not rounding theouter corner278 as much as theinner corner276, opening270 is easily extended farther radially toward theouter edge250. Similarly, by rounding theinner corner276 more than theouter corner278, opening270 does not extend as far inward towardend240. The particular benefits of shapingopening270 as described will be discussed further below.

As with thestator core190, eachlamination212 of thesegments210 is stamped from magnetic material. To reduce eddy currents, eachlamination212 is covered with an electrically non-conductive material. In the preferred embodiment, thelaminations212 are made of 2-3% silicon steel and coated with non-conductive coating, such as M36 steel with C5 coating manufactured by Temple Steel. Powered metal sintered segments with silicon may replace the thin laminations.

The shape of thesegments210 directs the flux lines emanating from the surfaces of themagnets220 to theouter surface250 of each of thesegments210.Magnets220 are of a type having sufficient magnetic strength to saturate or nearly saturate the material of each lamination comprising thesegments210 at theouter edge250. In addition,magnets220 are sufficiently heat resistant so as to not lose a significant amount of magnetism as therotor17 becomes hot (nearing 300 degrees Fahrenheit). In the preferred embodiment, themagnets220 are made of Neodymium-Iron-Boron (NdFeB) having an energy product (BHmax) of 30×10⁶(Gauss Ohersteds (GOe)). However, other magnets could be used in place of such preferred magnets. For instance, where greater temperature resistance is desired, Samarium-Cobalt (SmCo) magnets may be used. In general, given certain operating requirements such as maximum temperature and minimum flux, a particular magnet can be chosen.

Besides securing thesegments210, theopenings270 and thebars230 assist in directing the magnetic flux emanating from themagnets220 through thesegments210. In accordance with the invention, thebars230 are constructed of a material having high tensile strength which is both non-magnetic and electrically non-conductive. In the preferred embodiment, bars230 are made of pulltruded glass fiber with thermoset resin binder, commonly referred to as fiberglass. The pultrusion process orients the continuous glass fibers substantially parallel to the length of the bar. Although the preferred embodiment utilizes bars made of Class H fiberglass (suitable for use at 180° C.), bars230 could be made of any non-magnetic, non-conductive material having sufficient strength and weight characteristics. Being that thebars230 are electrically non-conductive, circulating currents are prevented, thereby improving the efficiency of themotor10. For example, there is no loss in efficiency due to the production of eddy currents. Further, thebars230 do not permit the circulating currents which might create an inductive rotor (squirrel cage).

With the structure of therotor17, including theopenings270 and using non-magnetic andnon-conductive bars230, it is believed that the magnetic flux emanating from the surfaces of themagnets220 is directed to generate an even distribution of magnetic flux across theouter surface250 of thesegments210. As noted above, such distribution is preferably strong enough to saturate the material of thesegments210 at theirouter surfaces250, thereby providing the maximum flux to link with thestator15. As shown in FIG. 2, magnetic flux present at theouter surface250 of thesegments210 crosses an air gap that is present between therotor17 and thestator15 to create a magnetic-circuit. By directing the magnetic flux as described, the flux crosses the air gap on substantially radial lines (with respect to the axis of rotation) and generates the maximum flux lines per area for maximum available torque. Accordingly, the distance that must be traveled by the flux is minimized as is the magnetic resistance as seen at the air gap.

At the position depicted in FIG. 2, a magnetic circuit begins at one of themagnets220. It is believed that the magnetic flux travels through one half of one of thesegments210, being directed by theopening270 and thebars230, to form an even distribution across one half of theouter surface250 of one of thesegments210. At that point, the magnetic flux crosses the air gap present between therotor17 and thestator15. To assist in directing the magnetic flux, theshaft80 is constructed of a non-magnetic material so that the magnetic flux of themagnets220 will not utilize theshaft80 as a means for completing a magnetic circuit, but will be directed outwardly toward theouter surface250 of thesegments210. Once across the air gap, the magnetic flux emanating from one-half of asegment210 links instantaneously with the equivalent of threeteeth200 of thestator15 and is linked to the next set of threeteeth200 of thestator15. The magnetic flux then links back across the air gap to one half of theouter surface250 of the adjacent one of thesegments210. From theouter surface250, the magnetic flux is directed through the adjacent one of thesegments210 to connect with the other side of the same one ofmagnets220 that the original magnetic flux lines emanated from, thereby completing the magnetic circuit. The retainer rings282 are of essentially the same construction as therings280.

FIGS. 2 and 2A shows that thebars230 do not fill theopenings270. As shown, small gaps are left near theinner corners276 andouter corners278 ofopenings270. The primary mechanical force contact between thebars230 and thesegments210 is along the innerangled surfaces272a,274aofopenings270, i.e., in retaining the segments against centrifugal forces. For this reason, theinner corner276 ofopenings270 has a greater radius of curvature than does theouter corner278 ofopenings270. Under normal conditions, the roundedinner edges232 ofbars230 can come in contact with theinner corner276 ofopening270. In such instances, the surface area available to transmit retaining force is increased over that which would exist if theinner corner276 were not rounded.

Theoutside corner278 ofopening270 has a radius of curvature that is smaller than theinner corner276. Optimally, theopening270 would not include an outer corner but would extend all the way to theouter surface250 in order to direct the magnetic flux lines as described above. However, in order to avoid complications in manufacturing, theopening270 is extended as far as permissible in a radial direction while still permitting the laminations of thesegments210 to be stamp formed. Additionally, theouter corner278 of theopening270 does not have to be rounded to the degree of the inner corner because the outer surfaces of opening270 do not encounter any forces.

Although the preferred embodiment includesbars230 generally having an elongated diamond shape, other shapes ofbars230 could be utilized. For example, a circular, triangular, etc. rod could be inserted inopening270. Of course, in the case whereopenings270 are shaped other than as elongated diamonds, thebars230 would be made in a shape that could fit through theopenings270 and must be of sufficient rigidity to support the segments.

FIG. 3 shows aretainer ring280 includingopenings290 and acenter hole300. Theretainer ring280 fits over theshaft80 and secures thebars230 in relation thereto.Retainer ring280 is made of non-magnetic material such as stainless steel, though other similar materials would suffice. Since theretainer ring280 also can be a lamination, several essentially identical plates are secured together to support and locate therods230. In the preferred embodiment, as with the other laminations, eachretainer ring280 is made of thin stainless steel plates which are covered with an insulative coating after being stamp formed. As further shown in FIG. 3, the retainer rings280 includenotches310 along their periphery. In one embodiment, thenotches310 are used to fusion weld several retainer plates together. In other embodiments, the retainer rings are cut from material of the total required thickness and, as a result,notches310 are eliminated and no fusion welding is required. Of course, where retainer ring plates are welded together, several other means of connecting them may be used.

Theopenings290 of the retainer rings280 are shaped slightly differently than theopenings270 of thesegments210. Unlike theopenings270, the primary mechanical forces exerted by the securingbars230 against the retainer rings280 are along the outer surfaces of theopenings290, i.e., in retaining thebars230 and thesegments210 andmagnets200 against centrifugal forces. Accordingly, the outer corners ofopenings290 have a larger radius of curvature than the inner corners to increase the engagement surface area of thebars230 therealong.

FIG. 4 shows a partial cross sectional view of an assembled rotor along line3—3 as shown in FIG. 2 with three sets ofsegments210 and two interior retaining rings at282. In a simpler preferred embodiment as in FIG. 1 where therotor17 is shorter, there is no need for the interior retainer rings282 and, consequently, they are not present. The securingbar230 extends the length of thesegments210 to connect with the retainer rings280 at either end of thesegments210 regardless of the number of sets of segments.

As described, the invention may be practiced utilizing differing numbers of sets of magnets (modules). Each magnetic module is approximately 2 inches long when the outside diameter of therotor17 being approximately 49.5 mm with retainer rings on either side. Although the magnetic modules are described in approximately two inch lengths, it is to be understood that other lengths, both smaller and larger could be utilized. Utilizing this modular approach provides motors (rotor of approximately 49.5 mm diameter) that optimally produce approximately 4 Nm of torque with one modular segment, 7 Nm of torque with two modular segments, 10 Nm of torque with three modular segments, 13 Nm of torque with four modular segments, etc. As is apparent, the available torque increases proportionally to the number of magnetic modules that are employed.

Abalance drive plate312 is provided at one end of the retainer rings280 to balance therotor17 by placingmaterial320, such as epoxy putty, on its inside rim314 (shown in FIG.1). In the preferred embodiment, thedrive plate312 is made of stainless steel or an equivalent non-magnetic material.

Near the other end of therotor17 is a clamp and lockscrew assembly330. As shown, theclamp340 screws onto theshaft80. in an axial direction where an outer surface of theshaft80 contacts an inner surface of theclamp340. The clamp provides threadedbores350 that align with the outside surface of the retainer rings280. A lock screw (not shown) is screwed into each bore350 to contact the retainer rings280 and compress the assembly of laminations into tight alignment.

FIG. 6 shows theshaft80 in its disassembled form. As shown, therear shaft360 and thefront shaft370 connect together to formshaft80 by means of a threadedscrew portion380 and a complementary threaded receivingportion390. Therear shaft360 includes ataper portion400 and aknurled portion410. As shown, the knurls of theportion410 extend in an axial direction along the outer surface of therear shaft360. Therear shaft360 additionally includes a threadedportion420 which accommodates the clamp and lockscrew assembly330 as described above. In the preferred embodiment, therear shaft360 is made of stainless steel or the like whilefront shaft370 is made of cold finish carbon steel or the like.

To manufacture therotor17, an assembly of retainer rings280 (and rings282 as necessary),segments210 andmagnets220 are aligned on guide means (such as guide pins) that extend through theopenings270 of thesegments210 and theopenings290 of the retainer rings280,282. Next, a cylinder having an inside diameter which is roughly equivalent to the diameter of thefinal rotor17 is inserted over the outside of the assembly. The cylinder pushes eachsegment210 towards the center axis until contact is made withmagnets220.

Next, thebars230 are inserted intoopenings290 of the retainer rings280,282 and through theopenings270 of thesegments210. As thebars230 are inserted, the guide pins are pressed out of the assembly. Thebars230 are tapered slightly at their lead ends to facilitate insertion into the assembly. Once thebars230 are inserted into the assembly, therear shaft360 is pressed into thecenter openings300 in the retainer rings280,282 and through the center opening formed by thesegments210 andmagnets220. Of course, the tapered end (seescrew portion380 and taperedportion400 in FIG. 6) of therear shaft360 is inserted into the assembly first. The components are sized such that theshaft sections400,410 force thesegments210 and retained magnets radially outward to firmly press the segments outwardly against thebars230 and thereby to press thebars230 outwardly into firm seating at the outer ends of theopenings290 in the retainer rings i.e., in a radial compressive relationship. This forms a prestressed rigid rotor structure. While being inserted, theknurl portion410 of therear shaft360 apparently assists in maintaining proper alignment of the various component parts and creates an interference fit with the laminations for transfer of torque similar to a spline.

Oncerear shaft360 is inserted, the assembly is removed from the cylinder and the receivingportion390 offront shaft370 is screwed onto therear shaft360 by means of the threadedportion380. Before thefront shaft370 is screwed onto therear shaft360, thebalance drive plate312 is welded to thefront shaft370 or secured by some other adequate means (see FIG.4). Then, after the front and rear shafts are assembled, set screws412 (see FIG. 1) are added throughbalance drive plate312 and into the adjacent retainer rings280. Next, after being thoroughly cleaned, a metal bonding adhesive is applied to the assembly to permeate and permanently bond the assembly. In the preferred embodiment, a polymer cement marketed asLoctite grade290 is used. With all of the component parts in place, the assembly is placed in a lathe or grinder, if necessary, and any extending portions along the outside surface of therotor17 are machined off. If such machining is required, then putty may be inserted into the air gap between theears260 of the segments to prevent metal fragments from accumulating. After the cement polymerizes, therotor17 is machined for a final time.

In accordance with the invention, it is believed that therotor17 acts as a solid body as a result of its construction, thereby exhibiting exceptional stiffness. In addition, therotor17 can be constructed of a small size while producing great magnetic flux at its outer surface and high torque.

Claims (22)

What is claimed is:

1. A rotor of cylindrical configuration for use in an electrical device, said rotor having a cylindrical outer peripheral surface and a central axis of rotation, comprising:

a rotor drive shaft in axial alignment with said central axis;

stacked laminations forming a plurality of magnetically conductive segments arrayed around said central axis with each of said segments spanning a circumferential sector of said cylindrical configuration and each having a radially outer surface and opposite end surfaces disposed generally normal to said central axis;

a magnet disposed radially of said rotor between each adjacent pair of said segments, each of said magnets having major planar side surfaces which extend generally radially of said rotor and face said segments on each side of the respective magnet, said magnets being magnetized through their thicknesses so that their magnetic poles are at said major planar side surfaces which face said segments, said magnets being so disposed that poles of the same polarity face each side of each of said segments;

said stacked laminations of each segment being connected with one another radially outward of said at shaft;

first and second abutment supports mounted on s aid drive shaft at opposite ends of said segments, said first abutment support being fixed to a portion of said drive shaft that is adjacent to one of said opposite end surfaces of said segments and providing an axially fixed support in abutment with said adjacent one of said opposite end surfaces, said second abutment support including a first portion that is in engagement with said shaft adjacent the other of said opposite end surfaces and secured in a predetermined axial position on said shaft by said engagement, and said second abutment support further include at least one abutment member that is movable axially of said shaft toward and away from the other of said abutment supports for compressing said laminations of said segments between said abutment supports and is in abutment engagement with said other of said opposite end surfaces and is axially supported in such abutment engagement for so compressing said laminations by said engagement of said first portion with said shaft, whereby said laminations forming said segments are compressed axially of said rotor between said first and second abutment supports in tight alignment solely by axial forces transmitted to said shaft by said first and second abutment supports; and

said segments, said abutment supports and said drive shaft there by forming a rigid rotor that provides high torque output in an electric device using said rotor.

2. A rotor as in claim1 and wherein one of said abutment supports is a drive plate, and one end of said compressed segments is attached to said drive plate.

3. A rotor as in claim1 and wherein each of said staked laminations is firmly seated against said drive shaft, and wherein said drive shaft, segments and supports interact as a single pre-stressed body.

4. A rotor as in claim3 wherein each of said magnets extends radially from closely adjacent said drive shaft to closely adjacent the outer periphery of said rotor.

5. A rotor as in claim4 including abonding adhesive permeating said rotor and bonding the components of said rotor together.

6. A rotor as in claim1 wherein each of said magnets extends radially from closely adjacent said drive shaft to closely adjacent the outer periphery of said rotor.

7. A rotor as in claim1 wherein said drive shaft is formed of a nonmagnetic material.

8. A rotor as in claim1 wherein said stacked laminations of each segment are so connected with one another by non-magnetic elements.

9. A rotor as in claim8 in which said connecting elements are electrically non-conductive.

10. A rotor as in claim1 wherein each of said segments is formed with an opening extending therethrough radially outward from said shaft and in generally parallel relation to said central axis and said laminations of each segment are connected to one another by non-magnetic securing bars extending through said openings.

11. A rotor as in claim1 wherein said drive shaft is a small diameter shaft and each of said laminations is firmly seated against said drive shaft.

12. A rotor as in claim11 wherein each of said magnets extends radially from closely adjacent said drive shaft to closely adjacent said outer periphery of said rotor.

13. A rotor as in claim1 wherein said first portion of said second abutment support has threaded engagement with axial threads on said drive shaft.

14. A rotor as in claim13 wherein said second abutment support includes a plurality of threaded abutment members extending generally parallel to said central axis and in threaded engagement with said first portion of said second abutment support.

15. A rotor as in claim13 wherein said first abutment support is welded to said drive shaft.

16. A rotor as i n claim1 wherein said first abutment support is welded to said drive shaft.

17. A rotor of cylindrical configuration for use in an electrical device, said rotor having a cylindrical outer peripheral surface and a central axis of rotation, comprising:

a rotor drive shaft in axial alignment with said entral axis;

stacked laminations forming a plurality of magnetically conductive segments arrayed around said central axis with each of said segments spanning a circumferential sector of said cylindrical configuration and each having a radially outer surface and opposite end surfaces disposed generally normal to said central axis;

a magnet disposed radially of said rotor between each adjacent pair of said segments, each of said magnets having major planar side surfaces which extend generally radially of said rotor and face said segments on each side of the respective magnet, said magnets being magnetized through their thicknesses so that their magnetic poles are at said major planar side surfaces which face said segments, said magnets being so disposed that poles of the same polarity face each side of each of said segments; said stacked laminations of each segment being connected with one another radially outward of said shaft;

a first support affixed directly to a portion of said shaft adjacent one of said opposite end surfaces of said segments and providing an axially fixed support in abutment with the respective adjacent end surfaces of said segments and thereby supporting said segments against movement axially of said shaft in one direction; and

a clamp and lock assembly affixed directly to said shaft adjacent the other of said opposite end surfaces of said segments, said clamp and lock assembly including a first portion and a second portion, said first portion abutting against the respective adjacent other end surfaces of said segments and being movable axially along said shaft for applying compressive force against said other end surfaces of said segments in said one direction, said second portion being affixed directly to a portion of said shaft adjacent said other end surfaces of said segments and axially supporting said first portion for maintaining such compressive force against said other end surfaces of said segments, whereby said laminations forming said segments are compressed axially of said rotor between said first support and said first portion of said clamp and lock assembly in tight alignment solely by axial forces transmitted to said shaft by said first and second abutment supports; and

said segments, said first support, said clamp and lock assembly, and said drive shaft thereby forming a rigid rotor that provides high torque output in an electric device using said rotor.

18. A rotor as in claim17, and including elements supported on at least one of said first support and said clamp and lock assembly and engaging into at least one end of said segments.

19. A rotor as in claim17 wherein said second portion of said clamp and lock assembly has threaded engagement with axial threads on said drive shaft.

20. A rotor as in claim19 wherein said first portion of said clamp and lock assembly includes threaded abutment elements extending generally parallel to said central axis.

21. A rotor as in claim19 wherein said first support welded to said drive shaft.

22. A rotor as in claim17 wherein said first support is welded to said drive shaft.

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